The Scientific Method• Scientists are always faced with the task of properly designing an experiment to test any and all variables. – Example: You decide to test what happens to a balloon when placed in a warm environment (like a moderately hot oven) versus what happens to a balloon placed in a cold environment (like the freezer).• Several important key terms in designing an experiment: – Constants - The variables that never change in the experiment. • Ex: The size of the balloon, the type of balloon, etc. – Control - The "normal" in an experiment. This is usually what you compare your experiment to. • Ex: A balloon placed at room temperature. – Independent Variable – The variable that you directly control. • Ex: Where you placed the balloon (oven or freezer). – Dependent Variable – The variable that changes because of the independent variable. • Ex: The size of the balloon
Covalent vs. Ionic Bonds• Know the difference between covalent and ionic bonds. – Covalent bonds are always between a non-metal and a non-metal. (groups 4-7) • Ex: CCl4 • These are ALWAYS referred to as molecules. – Ionic bonds are always between a metal with a non-metal. (groups 1-3 with groups 4-7) • Ex: LiF • These are usually referred to as compounds.
Naming Ionic Bonds• Name the cation first and the anion second.• Change the ending of the anion to –ide. – Ex: Name MgCl2 • Cation: Mg+2 magnesium • Anion: Cl-1 chloride – So the name is magnesium chloride• Note: You don’t have to worry about the subscripts. BUT MAKE SURE YOUR CHARGES= “0”• Do not forget your polyatomic ions.
Naming Covalent Molecules– 1: mono- • Covalent molecules are named in a– 2: di- similar fashion, except you must use– 3: tri- the prefixes you learned in class.– 4: tetra-– 5: penta- • Name the element as is placing the– 6: hexa- prefixes for the subscripts and change– 7: hepta- the ending to –ide.– 8: octa- – C4H10– 9: nona- • Tetracarbon decahydride– 10: deca- – NO2 • Nitrogen Dioxide
Mixtures• Mixtures are • Filtration combinations of substances that retain • Distillation their physical and chemical properties.• You can separate • Chromatography mixtures by using different techniques. • Crystallization• See if you can remember these separation techniques:
The Mole• The mole is the SI unit used to measure the amount of a substance.• You should be able to convert back and forth between atoms, moles, and grams.• You should be able to do this for elements and for compounds.• Remember this roadmap: Atoms moles mass (g)
Energy Diagrams • Energy diagrams show phase changes for a molecule. • These phase changes occur as a result of the relationship between temperature and energy. • Look at the diagram at the left and think of water and its phase changes.
Phase changes • Phase changes occur wherever there is a flat region in the diagram. • What happens to the molecules as you increase the temperature? • Think of the three states of matter and what happens to the molecules in these states.
Phases and Their Energies• As you increase the temperature, molecules gain more energy and break their attraction.• Look at the picture to the right to help you visualize the concept.
Reaction Rates• Chemists can increase the rate of reactions by doing one of several things: – Increase the temperature of the substance – Agitate the mixture – Increase the surface area of a substance – Decrease the volume of the container – Increase the pressure of the container
Reaction Rates• Reaction rates are related to the amount of collisions.• Temperature: As you increase the temperature, molecules move faster and collide more often.• Agitation: You are causing the molecules to collide as you mix them.• Increasing the surface area: Allows for more collisions to occur due to more space for them to occur.• Decreasing the volume of the container: There is less room for the molecules to move apart so they’ll run into each other more often.• Increasing the pressure: Molecules are more likely to collide.
Gas Laws• In order to solve any gas problems, you must remember the following equation: – PV = nRT• P = pressure• V = volume• n = number of moles• R = a constant and must be given• T = temperature